1. Field of the Invention
The present invention relates to a process for preparing isocyanatomethyl group-containing compounds by using a unique catalyst composition.
It is a primary object of the present invention to prepare, easily and economically, isocyanate compounds which are valuable as starting materials for the preparation of polyurethane materials, polyurea materials, polyisocyanurate materials and the like, all of which are valuable materials used widely in chemical industries, resin industries, paint industries and other industrial fields.
2. Description of the Prior Art
Various processes for the preparation of isocyanate compounds are known in the art. As an industrially important process, there can be mentioned a process in which an isocyanate is prepared from an amine or amine salt and a phosgene. Recently, a process for preparing an isocyanate from a nitro compound and carbon monoxide has been studied. Further, the reaction between an alkali cyanate and an organic halide has been known and studied for many years. This process was not very successful until so-called aprotic solvents such as DMF (dimethylformamide), DMSO (dimethylsulfoxide) or the like were developed. In 1957, Fukui et al found that isocyanuric acid esters and isocyanic acid esters, in some cases, can easily by synthesized under mild conditions in such an aprotic solvent, and since then, various compounds have been prepared by similar reactions. As processes using a catalyst in a non-protonic solvent, other than aprotic solvents, there can be mentioned, for example, a process using a tertiary amine or quaternary ammonium salt as a catalyst (U.S. Pat. No. 2,866,802), a process using a catalyst composition of phosphorus pentoxide and a weakly basic organic tertiary nitrogen compound (Japanese Patent Application Laid-Open Specification No. 36149/73) and a process for preparing an isocyanate from an .alpha.,.beta.-alkenyl halide in the presence of copper or a cuprous salt as a catalyst (U.S. Pat. No. 3,558,684). Generally speaking, the process of the present invention belongs to the latter type.
In the synthesis process for isolating an isocyanic acid ester by using a tertiary amine or quaternary ammonium salt as a catalyst, the catalyst is deactivated during the reaction and it is difficult to complete the reaction. Further, the amount of isocyanurate formed as a by-product increases as the reaction advances and the yield of the intended isocyanate is reduced. In the process using copper or a cuprous salt as a catalyst, it takes several to ten or more hours to complete the reaction, and in some cases, the starting halide is not completely consumed. Further as the reaction is extended, the amount of isocyanurate formed as a by-product increases and the yield of the desired isocyanate is drastically reduced. Another defect of this process is that because the boiling points of the starting halide and the desired isocyanate are very close to each other, if the halide is present, it is very difficult to separate the product from the starting halide. For this reason, the reaction must be essentially completed.